The following disclosure relates to determining the capacity remaining in the reservoir of an ink-jet printer""s service station.
Ink-jet printheads typically require frequent servicing to maintain print quality. A major element of the servicing program includes ink discharge (xe2x80x9cspittingxe2x80x9d) at frequent intervals. Spitting discharges low quality ink that may have partially dried or degraded due to the passage of time or exposure to the atmosphere. To maintain printhead health, spitting may be performed in a service station prior to printing, at intervals during printing, and before printhead capping at the conclusion of printing.
The volume of the reservoir into which the printheads spit can be a difficult design parameter. To avoid replacement of the service station during the life of the printer in which it is installed, the volume of the service station""s reservoir is typically somewhat oversized, in that it can accommodate more printhead servicing than is likely to result during the printer""s lifetime. However, the degree to which the reservoir is oversized may adversely affect other design parameters, such as cost, weight, size and shape. The liabilities associated with smaller service station reservoirs are equally great. In particular, the life span of some printers may be cut short and the cost of spare parts and repair may increase. An even greater liability associated with smaller service station reservoirs is that the firmware controlling the servicing of the printhead may have to be rewritten to result in less printhead servicing. This may result in added cost and degraded print quality.
One reason that the size of a service station""s reservoir is such a difficult design parameter is that the duty cycle, or rate of usage, of printers can vary widely. Where a printer has a lower duty cycle, it may be very desirable to service the printhead more often, although the printer is used less. The lower duty cycle may not result in sufficient ink movement to prevent drying and clogging, and the higher rate of servicing is required to prevent print degradation. Conversely, where a printer is used in a high duty cycle environment, less printhead servicing is required per page, but more pages are printed.
As a result, the firmware controlling key printer maintenance functions may base the amount of printhead servicing in part on the duty cycle of the printer. Unfortunately, the degree to which the service station reservoir is filled is an unknown variable. Accordingly, servicing of the nozzles within a printhead is performed at a non-optimum rate in most printers.
A system, method and apparatus for using an electrostatic drop detector (EDD) circuit within a printer to determine the remaining capacity of a service reservoir is described. Using information indicating the volume remaining for use within the reservoir, the rate at which printhead servicing is performed may be recalculated to result in more efficient use of resources.
An EDD circuit uses a high voltage electrical field to cause ink droplets to assume a charge by induction that is opposed to the charge within the reservoir. The electrical charge carried by the droplets per unit time results in current flow. Amplification of the current provides information on the number of ink droplets that resulted from the firing, which can then be compared against ideal results from firing a given pattern of nozzles. By firing nozzles, individually or in groups, in a series of bursts, all nozzles associated with one or more ink-jets may be tested.
According to one aspect of the method and apparatus to detect printer service station capacity, an EDD circuit and an associated method of operation provides information on both the condition of each printhead nozzle and also the remaining capacity of the reservoir portion of the service station. Due to the electrical conductivity of both wet and dry ink, an electric field extends from the surface of the ink within the reservoir. Upon arrival of the printhead within the service station area, the printhead is fired into the reservoir according to a firing pattern that tests each nozzle. The electrical charge carried by the ink droplets delivered in unit time results in the passage of an electrical current. Amplification of the current results in an output signal.
Information on the volume remaining within the reservoir and on the functionality of the nozzles of the ink-jet printhead may be obtained from examining the output signal. The output signal will have greater amplitude where all of the tested print nozzles are operational, and are delivering the expected number of charged ink droplets. Additionally, the signal will be stronger where the ink surface within the reservoir is closer to the firing nozzle; i.e. when the volume remaining within the reservoir is smaller. Additional information concerning the distance between the nozzle and the surface of the ink within the reservoir may be obtained by examination of the time delay between the firing burst sent to the printhead, thereby causing the nozzle firing, and the formation of the EDD output signal. A shorter time of delay between the firing burst and the formation of the output signal indicates a shorter flight path of the ink droplets, and a correspondingly smaller volume remaining within the reservoir.
Consequently, by examination of the shape, amplitude and delay time of the EDD output signal, the condition of the ink-jet nozzles and the volume remaining within the service station reservoir may be determined. By using information on the volume remaining, it can be determined if the rate of printhead servicing should be restricted due to a shortage of space remaining within the service station reservoir. Accordingly, more efficient balancing of the need to service the printhead with opposing design considerations is possible.